1. Field of Invention
The invention relates to a fan control device and a fan control method.
2. Related Art
Fans are disposed in various types of electrical devices to facilitate the heat dissipation in these devices. A conventional fan control device can properly set the rotation speed of the fan at a full speed, a low speed, and a medium speed between the full speed and the low speed according to the ambient temperature of the fan.
Referring to FIG. 1, a conventional fan control device 1 includes a temperature sensor 11 and a driving chip 12. The temperature sensor 11 measures an ambient temperature and generates a measurement value 111. The driving chip 12 generates a driving signal 122 according to the measurement value 111 or a threshold revolution signal 121. A fan 2 receives the driving signal 122 and works according to the driving signal 122. The driving signal 122 is a pulse width modulation signal, and the threshold revolution signal 121 is a constant voltage level, so the rotation speed of the fan 2 can be adjusted according to the voltage value of the driving signal 122 or the width ratio between the voltage pulses.
The temperature sensor 11 can be a thermistor, as shown in FIG. 2. The voltage of the measurement value 111 generated by the temperature sensor 11 gets lower as the ambient temperature gets higher.
As shown in FIGS. 1 and 3, the rotation speed of the fan 2 is adjusted according to the voltage value of the driving signal 122 or the width ratio between the voltage pulses, and the driving signal 122 changes according to the magnitude of the measurement value 111. Accordingly, the fan 2 can momentarily adjust the rotation speed in response to the ambient temperature.
Specifically, when the ambient temperature is higher than a temperature T1 and lower than a temperature T2, the driving chip 12 adjusts the voltage value of the driving signal 122 or the width ratio between the voltage pulses according to the measurement value 111, such that the rotation speed of the fan 2 can be adjusted according to the temperature variation.
When the ambient temperature is higher than the temperature T2, the driving chip 12 holds the voltage value of the driving signal 122 or the width ratio between the voltage pulses of the driving signal 122, which is not adjusted with the variation of the measurement value 111. As a result, the rotation speed of the fan 2 cannot be increased with the rising temperature when the fan 2 works at the full speed.
When the ambient temperature is lower than the temperature T1, the driving chip 12 generates the driving signal 122 according to the threshold revolution signal 121. The voltage value of the driving signal 122 or the width ratio between the voltage pulses of the driving signal 122 is not adjusted with the variation of the measurement value 111. Thus, the rotation speed of the fan 2 cannot be decreased with the dropping temperature when the fan 2 works at the low speed.
However, the conventional fan control device and method only can adjust the rotation speed of the fan with the variation of the temperature. In other words, the user cannot decrease the rotation speed of the fan leading to the noise of the fan, and cannot adjust the rotation speed of the fan according to the heat dissipating or airflow condition. That is, the conventional fan control device and method only can adjust the rotation speed of the fan according to the temperature variation. A fixed relationship between the rotation speed of the fan and the temperature is held, so the characteristic curve of the rotation speed of the fan versus the temperature cannot be further changed. Hence, the fan working at a fixed temperature has only one fixed rotation speed, and the rotation speed of the fan cannot be adjusted according to the user's requirement or the environmental condition at the fixed temperature.
Therefore, it is an important subject of the invention to provide a fan control device and a fan control method, which can automatically adjust the rotation speed of the fan according to the temperature as well as the user's setting. Thus, the rotation speed of the fan at various temperatures can be increased or decreased according to the user's requirement or the environmental condition such that the characteristic curve of the rotation speed of the fan versus the temperature can be further changed.